Heat the olive oil in a medium-sized saucepan over medium heat and add all the remaining ingredients. Stir well.
Simmer gently with the lid off for 45 minutes, or until the mixture has thickened and reduced by at least half. Remove from the heat, allow to cool and then blend until smooth. Season to taste and then transfer half to a sterilised glass jar to store in the fridge – use within two weeks. The other half can be stored in the freezer until needed.